Unfortunately, the two game systems are incompatible. I can't find it, but someone asked the same question in the SF2 forums and Wrench responded with the specific reasons why FE2 maps won't run properly in SF2. Damn shame really, as FE/FE2 still does a few things better than SF/SF2 - among them is the better looking maps at low altitude. That's one reason why I won't work in SF/SF2.
If the day ever comes when modders get access to the source code, what is needed is a third sim that combines the best of both - Strike Eagles.
Geezer's post in Looking for planes Vosges 2.0 was marked as the answer